Microvascular permeability and blood flow in atrial homografts in the hamster cheek pouch.

Atrial heart tissue grafts from newborn golden hamsters were transplanted into cheek pouches and were studied using intravital microscopic techniques. The smallest microvessels in the homografts showed a mean diameter of 13.3 +/- 1.1 micron (mean +/- S.E.M.) thus being in the dimensional range of terminal arterioles of the fourth branching order (A4, 14.0 +/- 2.1 micron) in normal cheek pouch tissue. Arteriolar red cell velocity was measured using a modified dual slit method. Volumetric blood flow was calculated and seen to be similar in terminal cheek pouch arterioles (116 +/- 34 pl/s) and in the graft vessels (119 +/- 26 pl/s). The responsiveness to topically applied norepinephrine of the graft vessels was found to be significantly lower than in cheek pouch arterioles. Microvascular permeability studied with FITC-dextrans (intravenous application) revealed significantly higher intensity values in the homografts as compared with the surrounding cheek pouch tissue. The difference was most pronounced for the largest tracer molecules used (Mw 150 000). This phenomenon is most probably due to an increased macromolecular permeability of the microvessels in the graft. The present findings point towards functional differences between the transplant vessels and cheek pouch capillaries.